Optical information record/playback systems have come into practical use for viable information data storage. With recent improvements in digital signal processing and data compression technologies, optical discs have been attracting much attention as evidenced by CD (compact disc) and DVD (digital versatile disc), for example, as archival devices of large capacity for recording computer programs, and music and image data. In addition, with a trend for lowering prices optical disc systems are coming into wider use for recording, and playing back (or reproducing) information using the optical discs.
Optical disc systems are generally configured to emit laser beams from a light source; record/erase information by irradiating the laser beams while scanning to form minute spots on a recording surface of an optical disc, which is provided with guiding tracks in the shape of either a spiral or concentric circles; and playback the information by detecting light reflected from the surface of the recording surface.
Incidentally, information on the optical disc is recorded in mark and space regions formed on the disc, which are different in reflectivity with one another. That is, by utilizing the difference in reflectivity in the mark and space regions, and the difference in length of the two regions and the combination thereof, the recording is attained on the optical disc.
Therefore, the power of light beams emitted from a laser device (which is hereafter referred to as power of beam emission or “beam power”) is controlled such that mark and space regions are formed respectively in predetermined locations during recording periods.
In regard to so-called recordable discs (or, write once-read many optical discs), which are formed with a recording layer containing organic dye compounds, such as CD-R (CD-recordable), DVD-R (DVD-recordable), and DVD+R (CD+recordable), recording marks are formed by heating with a relatively large beam power by causing the degeneration or decomposition of the dye compounds.
By contrast, space regions are formed without causing the degeneration or decomposition of the dye compounds by a smaller beam power which is comparable to the power during reproducing (or, playing back) periods. The mark regions, therefore, have a reflectivity lower than the space regions.
Incidentally, the beam powers for forming recording marks and space regions are called a recording power and a reproducing power, respectively.
Regarding the formation of the mark regions, the parameters pertinent to the laser beam such as pulse shape, for example, are adjusted according to the rule, called “recording strategy” related to the laser pulse shape, such that the thermal distribution along the track on the disc remains approximately the same even after the change in the length take place for the mark and spaces situated in front and behind of the mark.
In general, a light source drive circuit, which is configured to generate signals for driving the light source, is provided with registers for storing various setting parameters for determining the pulse shape of the driving signals. These parameters are set up in the registers prior to signal recording by means of the serial transmission (according to Japanese Laid-Open Patent Application No. 11-283249, for example).
It is noted that constant linear velocity (CLV) of the information track is achieved by variable angular velocity using higher rotational drive speeds on the inner tracks and lower speeds on the outer tracks. By contrast, CAV (constant angular velocity) mode is cited as another mode for recording information on the optical disc, in which a constant angular velocity of the information track is adopted for recording.
In most practical applications, since recording tracks are accessed randomly from an outer track to an inner track, or vice versa, with such a rapidity that it is quite difficult to adjust the rotation speed to constant linear velocity.
Because of the constant angular velocity, therefore, the CAV mode offers several advantages over the CLV mode such as, recording speeds higher than CLV mode, more ease of controlling the rotation of a spindle motor, and miniaturization of the motor. It is considered in practice that the CAV mode is suitable for downsizing, and reducing weight of, the optical disc recording apparatus.
Since linear drive speeds are lower on the inner tracks, while become higher on the outer tracks in the CAV mode, it is essential to optimize the beam power and the recording strategy addressing to the linear speeds and the change in speed (for example, Japanese Laid-Open Patent Applications No. 2000-82215, 2001-229564, 2002-208139, and 2003-281724).
In addition, with further increases in recording speeds, several difficulties are anticipated, in that the number of setting items, which are required for optimizing the beam power and recording strategy, tends to increase, and that the portion of the machine time of the control unit, which assumes overall control of the optical disc apparatus, is largely preempted by the process of optimizing setting items as long as relying on previous methods and apparatuses disclosed in the abovementioned applications; and this may adversely affect suitable servo control for the apparatus.
Moreover, although the time required for setting the setting items into the register may be reduced by utilizing the parallel transmission system (data bus, for example), this may result in the increase in costs as well as the size of the optical disc apparatus.